Frequency of a millimeter-wave ranges from 30 GHz to 300 GHz (the wavelength thereof ranges from 1 mm to 10 mm). In the electromagnetic spectrum, the location of the millimeter-wave frequency is between infrared and microwave. A millimeter-wave imaging system mainly has the following features: being sensitive to the shape and structure of an object, having a strong capability of distinguishing between a metal object and the background environment; having a high image resolution, thereby improving the capability of recognizing and detecting the object; the millimeter-wave being less vulnerable to hostile natural environment and being applicable in hostile environment with smoke and mist or the like as compared to infrared laser; having a small system volume and a light weight, and as compared to a microwave circuit, the millimeter-wave circuit size being much smaller, thereby making the millimeter-wave system easier to be integrated. Based on the aforesaid features, the millimeter-wave imaging technology has found wide application especially in fields of nondestructive testing and security inspection.
The millimeter-wave imaging mechanism is mainly divided into millimeter-wave active imaging and millimeter-wave passive imaging. The passive millimeter-wave imaging system has a simpler structure and a lower cost for imaging, but the imaging time is long and the imaging resolution is lower. In the active millimeter-wave imaging system, active synthetic aperture imaging and active holographic imaging are the main imaging mechanisms. The method of millimeter-wave holographic imaging is derived from the method of optical hologram, and it operates in the following way by using relevant principles of electromagnetic waves: first, a transmitter will transmit a millimeter-wave signal of a high stability, then a receiver receives echo signals reflected back from the object and processes the echo signals with a highly related reference signal to extract amplitude and phase information of the echo signals, thereby obtaining a three-dimensional image of the object in the scene by the method of data and image processing. The millimeter-wave image obtained by millimeter-wave active holographic imaging has a high image resolution and a short imaging time, and thus millimeter-wave active holographic imaging is particularly applicable to the human-body security inspection system.
In order to reduce scan time, the human-body security inspection system of millimeter-wave active three-dimensional holographic imaging current available is provided with two scan units, and as shown in FIG. 1, comprises: a first scan unit consisting of a first millimeter-wave transceiver 2 and a first millimeter-wave switch antenna array 7; and a second scan unit consisting of a second millimeter-wave transceiver 3 and a second millimeter-wave switch antenna array 8. The structure is specifically disposed as: two symmetrical rotating arms are disposed on a body frame of the human-body security inspection system to fix the two scan units respectively. The imaging method based on this human-body security inspection system comprises: when a to-be-tested person enters into the center of a to-be-scanned area, driving the two scan units to rotate by rotating a scan driving device 6, thereby performing rotary-scanning operation for the to-be-test person. An image processing device 5 obtains a three-dimensional holographic image of the to-be-tested person by synthesizing data from the two scan units.
As can be seen from the above description, the human-body security inspection system of millimeter-wave active three-dimensional holographic imaging current available has a complicated structure and the implementation cost is higher: and moreover, the two scan units perform scanning and information transceiving operation independently, so the image obtained has a low resolution.